The invention relates to a mirror-reflex camera having a viewfinder mirror which can be displaced linearly between a viewing position and a taking position, an electromagnetic drive being provided for displacing the viewfinder mirror.
Conventional devices may be gathered, for example, from DE 195 31 206 A1, U.S. Pat. No. 4,750,012 and U.S. 4,659,202. In these conventional devices, the electromagnetic drive for displacing the viewfinder mirror is constructed as an electric motor, or else as a moving-coil drive.
According to an embodiment of the present invention, a mirror-reflex camera comprises a viewfinder mirror that is linearly displaceable between a viewing position and a taking position and an electromagnetic drive for displacing the viewfinder mirror. The electromagnetic drive includes a permanent magnet arrangement permanently arranged on a housing side and a linearly displaceable plunger coil arrangement. The permanent magnet arrangement comprises at least one permanent magnet system having a magnet pot and a magnet core connected to and arranged radially in the magnet pot. A radial interspace is formed between the magnet pot and the magnet core in which flux lines of a magnetic field run radially. The plunger coil arrangement is axially displaceable.
One object of the present invention is to make available an improved electromagnetic drive which, in particular, permits reliable and quick displacement of the viewfinder mirror with a low outlay of energy.
This object is achieved according to the invention by virtue of the fact that the electromagnetic drive is formed by a permanent magnet arrangement permanently arranged on the housing side and a linearly displaceable plunger coil arrangement. The permanent magnet arrangement comprises at least one permanent magnet system which has a magnet pot and a magnet core which is arranged radially in the magnet pot and connected to it, there being formed between the magnet pot and the magnet core a radial interspace in which the flux lines of the magnetic field run at least essentially radially. The plunger coil arrangement is arranged in an axially displaceable fashion.
According to the invention, the electromagnetic drive is therefore utilized directly to displace the viewfinder mirror, it being possible to dispense with a complicated mechanical positive guidance and mechanical kinematics for deflecting the movement of the electric drive. As a result, the costs of production and assembly are reduced, durability is lengthened and the speed of the changeover operation is increased. Moreover, the outlay on energy for displacing the mirror is kept low. Since the total mass moved can be kept small, the mechanical loads on the moved parts as well as on the adjoining stationary ones are low during the processes of acceleration and braking. The outlay required for the electric supply is kept relatively low by the use of the permanent magnet arrangement; electric energy need only be supplied for the linear displacement of the plunger coil arrangement.
According to another embodiment of the present invention, use is made of a permanent magnet system with a magnet pot and a magnet core arranged radially in it, where the magnetic field lines run radially between the magnet core and the pot wall. In particular, the magnetic poles of the permanent magnet system are situated at the outer axial ends of the magnet core and the pot wall so that a closed magnetic field can be achieved, in which relatively little magnetic flux runs outside the permanent magnet system and interacts electromagnetically with the environment. An efficient utilization of the magnetic flux inside the permanent magnet system can be achieved by a plunger coil system arranged around the magnet core.
For this purpose, according to yet another embodiment of the present invention, it is advantageously possible to make use of two permanent magnet systems each having a magnet pot and radially inwardly situated magnet core which are arranged essentially in a mirror-symmetric fashion relative to one another and bear against one another with their axial ends. A high magnetic flux-line density is thereby ensured by the two permanent magnet systems in a central inner region of the permanent magnet arrangement.
The viewfinder mirror can be linearly displaced with the plunger coil arrangement via a mirror support fastened on the plunger coil arrangement. As a result, the total mass of the viewfinder mirror, mirror support and plunger coil arrangement that is to be moved is relatively low, since no further mechanical parts required, for example, for a deflecting movement or positive guidance, need to be moved as well and thus accelerated and/or braked. The mirror support can, for example, project through a cut-out or an elongated hole in the magnet pots, and thus permit a reliable connection between the plunger coil arrangement and the viewfinder mirror. In this case, the mirror support can also advantageously be used for feeding current, for example by a flexible conductor track, to the plunger coil arrangement, with the result that no further mechanical part is required for this purpose, as well.
The fact that the viewfinder mirror can be displaced rigidly with the mirror support and that the latter, in turn, can be displaced via the plunger coil arrangement, eliminates the requirement of having to provide some sort of flexible connections which can possibly lead to maladjustment of the viewfinder mirror, and thus of the entire optical system.
The plunger coil arrangement can be implemented, in particular, as a sleeve constructed concentrically about the magnet core, and a plunger coil winding arranged on the sleeve, preferably on the outside of the sleeve.
Further features of the invention form the subject matter of the claims and will be explained in more detail, in conjunction with further advantages of the invention, with reference to exemplary embodiments.